1. Field of the Invention
The present invention relates generally to a vibration damper with an adjustable damping force. The vibration damper includes a cylinder filled with a damping medium. In the cylinder, a piston rod with a piston is realized so that the piston can move axially. The piston divides the cylinder into two working chambers. The vibration damper also has a damping valve. The damping force of the damping valve can be changed by a magnetic force generated by a magnetic coil inside a magnetic return body acting on an armature against a spring force of at least one spring.
2. Background Information
German Patent No. 41 14 305 A1 describes a known vibration damper in which the damping force characteristic is determined essentially by the tuning of a spring which acts on a shutoff valve body. The dimensions of the pressurized surfaces also have an essential influence on the opening action of the damping valve.
One characteristic of this known valve is that it has damping force characteristics which are relatively flat and which run essentially parallel to one another in the range of higher flow velocities of the damping medium. In this context, reference is made to German Patent No. 41 04 110 A1, FIG. 13. A major problem with these known valves is that they are relatively sensitive to tolerances, which means that significant time, effort and expense must be devoted to their regulation and adjustment. Recently, it has become possible to adjust the biases of one or more springs of the damping valve, as a result of which the characteristics can be shifted, within limits.
German Patent No. 38 00 288 C1 describes a valve arrangement for a hydraulic adjustable vibration damper in which a correct magnetic flux can be established by means of a clamping screw or tension screw. This design is based on an air gap in the path provided for the magnetic flux. The air gap represents a resistance, the action of which reduces the effect of the force of the magnetic coil. If the air gap can be neutralized, overcome or bridged, the magnetic force provided becomes available.
German Patent No. 40 23 828 A1 describes a method for regulating, setting or tuning a valve in which a valve assumes a switching function in the opening direction for a valve body.
The valve is designed, within a defined opening phase, to allow a specified quantity to flow through. A parameter for the achievable flow amount is that the opening movement must take place as quickly as possible. For that purpose, a minimum magnetic force is necessary to lift the valve body against the force of a spring. If the required minimum force is not achieved, only the resistance to the magnetic flux is set.